www.air-worldwide.com Effects of Strong Motion Processing Procedures on Time Histories, Elastic and Inelastic Spectra By Paolo Bazzurro, Brian Sjoberg, Nicolas Luco (AIR) Walter Silva, Robert Darragh (Pacific Engineering and Analysis) Presented at COSMOS INVITED WORKSHOP ON STRONG-MOTION RECORD PROCESSING Richmond, CA, May 26-27, 2004
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www.air-worldwide.com
Effects of Strong Motion Processing Procedureson Time Histories, Elastic and Inelastic Spectra
By Paolo Bazzurro, Brian Sjoberg, Nicolas Luco (AIR)
Walter Silva, Robert Darragh (Pacific Engineering and Analysis)
Rupture Distance VS30 HP LP Xcos() or DMFEarthquake Year Mag Mechanism (km) Station Name (m/s) (Hz) (Hz) Ycos()Imperial Valley 1979 6.5 S 8.5 Brawley Airport 209 0.10 40 0.7 1.05-1.54
1 El Centro Array #6 203 0.10 40 0.5 1.00-1.08
0.6 El Centro Array #7 211 0.10 40 0.5 1.00-1.08
14.2 Parachute Test Site 349 0.10 40 0.7 1.05-1.54
Loma Prieta 1989 6.9 R (oblique) 6.1 LGPC 466 0.10 0.8 1.04-1.17
Summary of Effects of Processing Techniques on Elastic and Inelastic Spectra
In general, effects are larger for inelastic than for elastic spectra and for longer periods at any given response level (i.e., R=1 through 8)
Causality of the filter does not systematically affect the amplitude of the spectra. The statistical impact on spectra due to the filter order is negligible Increasing the value of the HP cut-off frequency, fHP, generates inelastic spectra
that are systematically lower at periods much lower than 1/ fHP regardless of the causality of the filter. This can be in part explained by the lengthening of the effective period of vibration of structures in the post-elastic regime.
Records with residual displacement offset preserved generate inelastic response spectra that are consistently higher than those caused by records with offset removed. (Phenomenon observed for 6 fault-normal records only).
NOTE: See paper for effects on spectra caused by applying a filter to simulated ground motion records
Summary of Effects of Processing Techniques on Ground Motion TH’s
In general, effects are significant for PGD and, to a lesser extent, for PGV. The impact on other parameters (e.g., PGA, Arias Intensity, and duration) is negligible.
Causally filtered records have PGV and PGD values that are, on average, smaller (by 5-10% and 5-15%, respectively) than those of acausally filtered ones.
Acausally filtered records generally display a more prominent ramp of increasing displacement prior to the onset of strong-motion than causally filtered records. Peak-to-peak displacement amplitude, however, is similar for each processing technique.
The filter order does not affect the ground motion parameters considered here. Increasing the value of the HP cut-off frequency, fHP, generates records with
lower PGV and PGD values (5% and 15-20%, respectively), as expected. The values of PGV and PGD are considerably larger (5-20% and 50-60%,
respectively) in records with residual static offset preserved, as expected.